Many of the polymer surfaces stated or of the paper surfaces finished for particular gloss, such as are required, for example, for high-value printed products, have particularly smooth, low-absorbancy surfaces, with the consequence that adhesive bonds made to them can be unreliable, especially when the bonds are produced by applying limited pressure for only a very short time. But these are exactly the kind of adverse conditions affecting the flying splice connections that are required from time to time, where the pressure application time—the machines, of course, are not stopped but instead continue to run at full speed, which in papermaking can be up to 130 km/h (that is, around 36 metres per second)—is measured in only fractions of a millisecond and where the application pressure cannot be too high since otherwise the resistance of the reel to the press rolls would be too great and could cause tearing.
For the last-mentioned, very demanding utility a multiplicity of adhesive tapes with a very wide variety of adhesives have already been made available, the recommendation generally being for precise matching of the adhesive and the article to be bonded and in particular its surface material and surface roughness. Very generally, however, it may be stated that, in order to be suitable for the flying splice of polymeric films and coated papers, adhesives must have a high initial tack, in order to bond with sufficient reliability to the outgoing web at the prevailing speeds.
As well as the abovementioned applications in the papermaking and paper-converting industry, and also in the film-producing industry, which are of particular focus here, there are also, however, other applications for adhesives of high initial tack or tackiness, as for example for the sealing of certain forms of mass packaging. The flying splice technique is for the present-day adhesives industry comparable with what space travel was, 40 years ago, for mechanical engineering; consequently it seems appropriate not to restrict protection for the adhesives disclosed herein to the flying splice utility alone.
For a static splice (i.e. one performed at standstill) as well the adhesive bonding of particularly smooth papers, especially when they are coated, is difficult. Although in this case the pressure application time can be significantly longer, experience indicates that in many cases even this provides no further assistance.
For both flying and static splice it is common to use acrylate-based adhesives. These have the disadvantage, however, that they do not adhere, or adhere inadequately, to materials having a particularly smooth surface, such as PE-coated papers or gravure papers, for example, and the splice fails.
In order to allow a sufficient bonding with known adhesive tapes despite this, the conceptually most simple but economically often most painful measure is to enlarge the bond area. Another possibility is to use liquid adhesives rather than adhesive tapes. The inevitable corollary of using liquid adhesives, however, are the high personnel costs arising from lengthy manual operation, and solvent vapours, with all of their adverse consequences for the environment in general and one's own staff in particular.
The invention is based on the object of providing a high-tack adhesive. This adhesive should preferably provide such a large shear stability time that it is suitable even for producing adhesive splicing tapes that are able to compete—including not least on coated materials—with liquid adhesives without the need to go to extreme tape widths.